Glaucoma is a leading cause of blindness in the world. Indeed, over 2.5 million people in the United States suffer from the disease, and millions more are at risk of developing glaucoma. As the population ages, the number of individuals suffering from glaucoma will continue to grow since the elderly are being affected disproportionally.
Based on the etiology of glaucoma, it can be classified into primary and secondary glaucoma. Primary glaucoma, also known as congenital glaucoma, can occur in the absence of other ocular conditions, and its underlying causes are not known. It is known, however, that increased intraocular pressure (IOP) observed in primary glaucoma is due to the obstruction of aqueous humor flow out of the eye. Secondary glaucoma results from another pre-existing ocular disease such as uveitis, intraocular tumor, enlarged cataract, central retinal vein occlusion, trauma to the eye, operative procedures and intraocular hemorrhage. Generally, any interference with the outward flow of aqueous humor from the posterior chamber into the anterior chamber and subsequently into the canal of Schlemm can lead to secondary glaucoma.
Current treatments for glaucoma aim to reduce the pressure in the eye by decreasing the amount of aqueous fluid being produced or alternatively by enhancing the flow of fluid out of the eye by using mechanical means. Agents for topical application used to treat glaucoma include miotics (e.g., Isopto® Carpine, Ocusert®, Pilocar®, and Pilopine®) and epinephrines (e.g., Epifrin® and Propine®), which increase the outflow of fluid; beta blockers (e.g., Betagan®, Betimol®, Betoptic®, Ocupress®, Timoptic®, Optipranalol®); carbonic anhydrase inhibitors and alpha andrenergic agonists (e.g., Alphagan®, Iopidine®, Trusopt®), which reduce the amount of fluid; and prostaglandin analogs (e.g. Lumigan®, Rescula®, Travatan®, Xalatan®), which increase the outflow of fluid through a secondary drainage route.
The topical application of ophthalmic compositions for the treatment of glaucoma requires penetration of the drug through the cornea and into the anterior chamber, which contains aqueous humor, which then drains into the conventional outflow pathway. Intraoccular pressure is lowered by drugs acting in the Schlemm's canal and the uveal-scleral pathway. Penetration of the drug through the cornea requires a balance of hydrophobic and hydrophilic characteristics. In order to diffuse into the cornea the drug must be sufficiently soluble in non-polar media, and it must be sufficiently soluble in aqueous media in order to diffuse out of the cornea into the aqueous humor.
Potentially useful drugs for the treatment of glaucoma can be delivered as prodrug esters. The use of prodrug esters, which are cleaved enzymatically (e.g., in the cornea) to regenerate the active compound, can enhance penetration of the drug through the cornea into the anterior chamber. However, many esters are too hydrophobic to diffuse out of the relatively non-polar external layer of the cornea into the aqueous humor. Furthermore, such compounds are often not sufficiently soluble to formulate in aqueous solutions. Accordingly, there is a need in the art for ophthalmic compositions having the capability to penetrate through the cornea into the anterior chamber. At the same time such compositions need to exhibit sufficient hydrophilic properties to formulate in aqueous solution and to be soluble in the anterior chamber. Provided herein are compositions and methods addressing these and other needs in the art.